# Pythagoras' Theorem in geometry question.

• Nov 18th 2011, 02:49 PM
Kyleee
Pythagoras' Theorem in geometry question.
Sophie built a small tower, made of bricks, in her back garden. On top of it she fitted a large glass light-bulb holder.

The diagram shows it as part of a circle.

Centre, C, is 20 centimetres above the top of the wall.

1. Calculate the radius of the circular bulb holder.

2. Use this to find the total height of the structure.

Here's the diagram :
• Nov 18th 2011, 02:59 PM
skeeter
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
radius of the circle is 20 cm (you really need to have a look at the definition of a radius)

total height = height of the wall + diameter of the circle
• Nov 18th 2011, 03:00 PM
e^(i*pi)
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Quote:

Originally Posted by Kyleee
Sophie built a small tower, made of bricks, in her back garden. On top of it she fitted a large glass light-bulb holder.

The diagram shows it as part of a circle.

Centre, C, is 20 centimetres above the top of the wall.

1. Calculate the radius of the circular bulb holder.

2. Use this to find the total height of the structure.

Here's the diagram :

Unless I'm missing something obvious isn't the radius 20cm?
• Nov 18th 2011, 03:02 PM
Kyleee
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Just to let you guys know : I know what the radius is (half the diameter of a circle), but my teacher said it's an exam question and I'm in the highest maths class. How the heck can it be that easy?
• Nov 18th 2011, 03:04 PM
Kyleee
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Quote:

Originally Posted by skeeter
radius of the circle is 20 cm (you really need to have a look at the definition of a radius)

total height = height of the wall + diameter of the circle

I also thought of this too, but I didn't really think this was correct. I think I've did something like this before and I did it like the way you've just said it and I got it wrong. D:
• Nov 18th 2011, 03:04 PM
Kyleee
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Sorry guys, the diagram is wrong, i'll upload the correct one in a minute. :D
• Nov 18th 2011, 03:10 PM
Kyleee
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
There! New diagram up; now can you help me? :D
• Nov 18th 2011, 03:35 PM
skeeter
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Quote:

Originally Posted by Kyleee
There! New diagram up; now can you help me? :D

one word for you ... Pythagoras.
• Nov 18th 2011, 03:38 PM
Kyleee
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Skeeter, I know it's pythagoras (that's what my teacher said), but where are the triangles? Please help, I really need to do this. D:
• Nov 18th 2011, 03:43 PM
skeeter
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
$r^2 = 22^2 + 15^2$
• Nov 18th 2011, 03:53 PM
Kyleee
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Quote:

Originally Posted by skeeter
$r^2 = 22^2 + 15^2$

Okay, I know this now, thanks.
But now I need to do question 2 : find the height of the whole thing.

Would I just double the answer and add it to 55? Orrrr...

Edit : Okay, that's totally wrong what I just said. I got muddled up. :P

Would I just do 20 + 55 + ? =
• Nov 18th 2011, 05:42 PM
skeeter
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Quote:

Originally Posted by Kyleee
Okay, I know this now, thanks.
But now I need to do question 2 : find the height of the whole thing.

Would I just double the answer and add it to 55? Orrrr...

Edit : Okay, that's totally wrong what I just said. I got muddled up. :P

Would I just do 20 + 55 + ? =

where did 20 come from?
• Nov 18th 2011, 05:55 PM
Wilmer
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
Well, it's obvious to me that the line shown as 22 is really 20;
that makes radius = sqrt(15^2 + 20^2) = 25.
So height = 55 + 20 + 25 = 100.
All in favor raise your hands !!
• Nov 18th 2011, 10:32 PM
Deveno
Re: Please help with this maths question, it's quite easy, I just don't know it. :D
the diagram and the wording of the problem are inconsistent. this should be resolved.